Electrostatic separator



Dec. 19, 1961 1 c. A. PHILLIPS 3,013,662

ELECTROSTATIC SEPARATOR Filed June 12, 1959 2 Sheets-Sheet 1 INVENTOR CHARLES APHILLIPS E BYMYgWh) ATTORNEYS.

Dec. 19, 1961 c. A. PHILLIPS ELECTROSTATIC SEPARATOR 2 Sheets-Sheet 2 Filed June 12, 1959 INVENTOR CHARLES A.P|-||LuPs B MY E ATTORNEYS surface layer.

3,013,662 ELECTRGSTATIC SEPARATGR Charies A. Phillips, Delia, Alberta, Canada Filed June 12, 1959, Ser. No. 81?,862 Gaines priority, application Canada Apr. 16, 1959 6 Claims. (Cl. 209-429) This invention relates to a method and a device for separating the components of a mixture of solid materials. In particular, the invention relates to an electrostatic method device for separating finely divided gold from the sand and gravel of placer deposits.

Placer deposits of gold are characterized in that the gold is neither mechanically nor chemically associated with the minerals of the gangue material in which it is found. The gangue material varies from fine sand to coarse gravel and the gold varies from fine dust to large nuggets. There are many known methods of extracting gold from sand and gravel varying from panning and sluice box methods in small scale operations to hydraulicking, dredging, and steam shovel or drag line work with subsequent amalgamation of the gold with mercury in large scale operations. However, all known commercially successful methods of treating placer gold deposits are characterized in that they require water in amounts which commonly range from 1 ton to or 6 tons of water per ton of ore treated. Where water is not immediately available the cost of transporting it to the site of the placer deposit is often so excessive that the gold cannot be extracted economically. As a result, many known placer deposits of gold cannot be worked at a profit and either have never been exploited or have been abandoned after a short period of operation.

It is the purpose of the present invention to provide a method and an apparatus for extracting gold from sand and gravel placer deposits without using water. This is accomplished by making use of the differing responses of the components of the placer ore to the attraction of an eiectrostatically charged surface. Such a method and apparatus may also be adapted to separate the components of any mixture of solid materials.

The invention in its broadest aspect resides in a method of separating finely divided gold from associated gangue material. In the method, starting material is fed onto a rotating drum having a surface layer of electrostatically non-conducting material. A non-fluctuating static electric charge is applied to the surface layer. A current of air is directed onto the surface layer, at a point displaced rotationally with respect to the drum from the point of contact of the starting material with the surface layer, to remove less strongly attracted gangue material from the The more strongly attracted gold is removed from the surface layer of the drum, and collected, at a point displaced rotationally with respect to the drum from the point of impingement of the current of air on the surface layer.

The apparatus of the invention consists of a frame and a rotatable drum mounted on the frame. The drum has asurface layer of electrostatically non-conductive material and means, preferably a buffer, associated with the surface layer applies a non-conductive static electric charge to it. Means such as a chute feeds starting material onto the surface layer. Blower means positioned adjacent the drum is adapted to direct onto the surface layer, at a point displaced rotationally with respect to the drum from the point of contact of the material with the surface layer, a current of air adjustable to remove less strongly attracted gangue material from the surface layer. The means associated with the surface layer of the drum for applying the static electric charge is positioned at a point displaced rotationally with respect to the drum from the point of contact of the current of air on the surface "ice layer and is adapted to remove the more strongly attracted gold from the surface layer. Additional means collects the gold thus removed.

In the drawings which illustrate an embodiment of the invention,

FIGURE 1 is a front view of an electrostatic separator;

FIGURE 2 is a rear elevation of the separator of FIG- URE 1;

FIGURE 3 is a plan view of the separator of FIGURE 1; and

FIGURE 4 is a vertical section along the line 4-4 of FtGURE 3.

FIGURES l and 2 illustrate the exterior form of the apparatus and show the manner in which the several moving parts are interconnected and mounted on the frame it A vibratory screen 11 is mounted on top of frame 10 and the material to be separated is fed. onto screen 11 and the separated components emerge from outlets 12, 13 and 14. A detailed description of FIGURES 1 and 2 will be given later during the discussion of the machine in operation.

Turning now to FIGURE 4, the essential components of the apparatus comprise a rotatable drum 20, a buffer belt 21 and an air tube 22 for directing a current of air on the surface of drum 20. The latter surface consists of a layer of polyethylene plastic. However, this surface layer may alternately be formed of any suitable electrically non-conducting material capable of holding a static electric charge. Of course buffer belt 21 should be of a material suitable, with respect to the surface layer of drum it), to set up the electrostatic charge, for example a cotton belt. If drum 2t and butter belt 21 are rotated in the same direction e.g., clockwise they will, in fact, be travelling in opposite directions over the area in which the two are in contact. Accordingly, there is sufficient :riction between them to set up and maintain an electrostatic charge on the surface of the drum. By making use of well known principle that different materials will be attracted to such a charged surface to different degrees,

the separation of those different materials is effected.

Thus, it has been found that gold may be separated from sand and gravel of placer deposits because the gold is more strongly attracted to the charged surface layer of the drum than are the other minerals making up the sand and gravel.

Referring in detail to FIGURE 4, it will be seen that screen '11 comprises a base plate 25 from which the center portion has been cut out to provide an opening over which the screening material 26 is placed. A plurality of rods 27 extend across the opening to support the screening material. Base plate 25 supports two upstanding side walls 28 between which extends a deflector plate 29. Screen 11 is freely mounted on top of the frame and is caused to reciprocate in the manner which willbe described below. Screen 11 serves to separate the coarse aggregate which is drawn oif by means'of'chute 30 to outlet 14. The fine aggregate drops through the screening material 26 into hopper 31 which is provided with a slot-like opening 32 at its bottom. Opening 32 extends the full length of drum 20 and is provided with a gate 33 for adjusting its width. A helical screw 34 is provided adjacent opening 32 to assist the movement of the fine material therethrough. It has been found that some of the particles falling onto the surface of drum 20 from opening 32 occasionally rebound from the surface and are thus only momentarily exposed to the electrostatic charge on the surface. Accordingly, someparticles which would normally adhere to the charged surface are lost.

I To prevent this, a deflector plate 35 is arranged as shown which serves to divert the erratic particles back onto the surface of the drum to insure that they are adequately exposed to the electrostatic charge. 'j

Positioned below deflector plate 35 and adjacent drum is a magnet 36. It has been found that the minor magnetic material occurring in most placer sands is attracted to an electrostatically charged surface to the same degree as gold. Therefore, by exposing those particles adhering to the charged surface to a strong magnetic attractive force the magnetic particles are separated therefrom.

Air tube 22 is positioned as shown below magnet 36 and also adjacent the surface of drum 20. Air tube 22 extends the full length of drum 20 and is provided with a plurality of apertures in its upper side. Air is forced through the tube and passed through the apertures to impinge on the surface of drum 20. To assist in directing the air onto the surface of drum 20, a plate 37 is arranged as shown. The provision of this means to direct a current of air on the surface of drum 20 is essential to the invention. By carefully adjusting the force with which the current of air impinges on the surface of the drum all the material adhering to the electrostatic charge on the drum, other than gold, may be removed from the drum. As stated above, it has been found that gold is more strongly attracted to the electrostatic charge than the other materials making up the sand and it is by taking advantage of this fact that the separation is made. However, it has been found that some of the finer particles of gangue material, although not as strongly attracted to the charged surface as the gold, are, nevertheless, attracted and therefore adhere to the surface simply because they are so light in weight and, therefore, can be held by a weaker attractive force. Accordingly, the blower means is provided to remove these gangue particles from the drum by causing a current of air to impinge on its surface causing these light and less strongly attracted particles to fall off whereupon they are caught by chute 38 and led off to outlet 13. It will be seen, therefore, that any two materials which are attracted to an electrostatically charged surface to different degrees may be separated by first attracting both materials to the charged surface and then removing from the surface the less strongly attracted material by means of a current of air.

Referring still to FIGURE 4, it will be seen that buffer belt 21 is engaged on three rollers 40, 41 and 42. Roller 40 is a driver and rollers 41 and 42 are idlers. Means is provided to shift the position of idler 41 in order to maintain the proper tension in belt 21. The width of belt 21 extends the full length of drum 20 so that the whole surface of the drum is charged. Besides setting up an electrostatic charge on the surface of drum 20, buffer belt 21 has a secondary purpose which is to remove the gold adhering to the drum in order to cause it to drop through outlet 12. To accomplish this, buffer belt 21 must be run in a clockwise direction (as shown in FIGURE 4) when drum 20 is rotated in a clockwise direction. In other words, the direction of belt 21 is opposite to the direction of drum 20 over the area in which the two are in contact.

Referring again to FIGURE 2, the apparatus operates as follows. The main drive pulley 45 is connected to an external source of power suchas a gasoline motor by means of a drive belt 46. Coaxial with and mounted behind pulley 45 is a step-down pulley 47 having a drive belt 48 engaged thereon. Belt 48 extends around pulleys 49 and 50. The shaft of pulley 45 is connected to roller 40, thereby driving belt 21. Pulley 49 carries a pin 51 to which one end of a crank rod 52 is rotatably attached. The other end of crank rod 52 is pivotally attached to one end of arm 53 which itself is pivotally attached at 54 to frame 10. The other end of arm 53 is bifurcated to receive pin 55 fixed to screen 11. As pulley 49 rotates, crank rod 52 causes arm 53 to pivot about point 54 thereby causing a reciprocating action to screen 11. By reference to FIGURE 1 it will be noted that a similar arrangement of parts is placed on the opposite side of the apparatus.

Idler roller 41 may be shifted, as mentioned above, by

means of the adjusting mechanism 56. The shaft 57 of roller 41 extends through a slot in each side wall of frame 10 and is mounted for rotation in a hole in adjusting mechanism 56. The latter mechanism is fixed to the sides of frame 10 by a nut and bolt extending through a hole in the side of said frame 10 and through one of a series of holes in adjusting mechanism 56.

The shaft 60 of pulley 45 (and the associated pulley 47) extends through frame 10 to the other side of the apparatus where a sprocket wheel 61 is rigidly fixed thereto. Engaged around sprocket wheel 61 is a chain 62 which is also engaged about a second sprocket wheel 63 mounted on the shaft 64 of drum 20. Shaft 65 of pulley 50 extends through the frame 10 to the opposite side of the apparatus where an impeller wheel 66 is attached to it. Impeller wheel 66 is enclosed within a jacket 67 which serves to direct the current of air caused by the rotation of the impeller Wheel to flow through tube 22 and thus onto the surface of drum 20. Jacket 67 is provided with a semi-circular aperture through which the outside air is sucked in.

Shaft 70 of magnet 35 is mounted in the side walls of frame 10 as shown in FIGURES l and 2. In the particular embodiment of the invention shown, an electromagnet is used although it will be appreciated that a permanent type magnet could also be used. It has been found that it is only necessary to clean magnet 36 occasionally so that means has been provided whereby it may be taken out and cleaned by hand. However, if the percentage of magnetic material in the sand being processed is unusually high it may be preferable to provide means whereby the magnet is cleaned continuously. This may be done by rotating the magnet and providing a scraper blade adjacent thereto to remove the magnetic material as it is picked up.

What I claim as my invention is:

l. A device for separating finely divided gold from associated gangue material, comprising a frame, a rotatable drum mounted on the frame, a surface layer of electrostatically non-conducting material on the drum, means for feeding starting material onto said surface layer, means associated with the surface layer of the drum for applying a non-fluctuating static electric charge to said surface layer, blower means positioned adjacent the drum and adapted to direct onto the surface layer, at a point displaced rotationally with respect to the drum from the point of contact of the material with the surface layer, a current of air adjustable to remove less strongly attracted gangue material therefrom, said means associated with the surface layer of the drum being positioned at a point displaced rotationally with respect to the drum from the point of contact of the current of air on the surface layer and adapted to remove the more strongly attracted gold therefrom, and means to collect the gold thus removed.

2. A method of separating finely divided gold from associated gangue material, comprising the steps of feed ing starting material onto a rotating drum having a surface layer of electrostatically non-conducting material, applying a non-fluctuating static electric charge to said surface layer, directing a current of air onto said surface layer, at a point displaced rotationally with respect to the drum from the point of contact of the starting material with the surface layer, to remove less strongly attracted gangue material therefrom, and removing and collecting at a point displaced rotationally with respect to the drum from the point of impingement of the current of air on the surface layer, the more strongly attracted gold from the surface layer of the drum.

3. An electrostatic separator as claimed in claim 1, in which said means for applying said charge to the surface layer of said drum comprises buffing means in contact with said surface layer, said buffing means acting to remove the more strongly attracted gold from the surface layer of the drum.

4. An electrostatic separator as claimed in claim 3, in which said bufling means comprises a moving buflfer belt adapted to travel in a direction opposite to the direction of rotation of said drum in the area of contact with said surface layer.

5. An electrostatic separator as claimed in claim 1, including magnet means arranged adjacent said drum between said feeding means and said blower, of such prox imity as to extract any magnetic material from the material adhering to the charged surface layer of said drum.

6. An electrostatic separator as claimed in claim 1, including deflector means fixed to said frame adjacent said drum and said feeding means adapted to deflect back '6 I into the surface of the drum any material fed from the feeding means which rebounds from said surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,355,477 Howell Oct. 12, 1920 2,094,440 Weis Sept. 28, 1937 2,314,939 Hewitt Mar. 30, 1943 2,548,771 Carpenter Apr. 10, 1951 2,737,348 Roberts Mar. 6,, 1956 2,786,636 Oishi Mar. 26, 1957 FOREIGN PATENTS 2,981 Great Britain AD. 1881 

